Method for making a magnetic recording disk having a corrosion-protective layer of a perfluorinated polyether acid

Abstract

A process is provided for synthesizing metal salts of perfluorinated polyethers containing at least one carboxylic acid group. The polymeric salts so provided are effective as anti-wetting and corrosion-protective agents. The metal salts of perfluorinated polyether acids may be used to prepare corrosion-protected substrates, including magnetic recording disks and magnetic recording heads.

1. A method for making a magnetic recording disk comprising:
 (a) forming an underlayer on a disk substrate;  
 (b) sputter-depositing a magnetic layer onto the underlayer;  
 (c) sputter-depositing a carbon overcoat onto the magnetic layer, said carbon overcoat having pinholes therein exposing the magnetic layer; and  
 (d) applying to the carbon overcoat a corrosion-protective composition containing a corrosion-protective agent comprised of a metal salt of a perfluorinated polyether having at least one carboxylic acid group, a metal salt of a partially hydrogenated perfluorinated polyether having at least one carboxylic acid group, or a mixture thereof, thereby filling any pinholes in the carbon overcoat with the corrosion-protective composition.  
 
     
     
       2. The method of  claim 1 , wherein the magnetic layer is comprised of a metal, a metal alloy, or a metal oxide. 
     
     
       3. The method of  claim 2 , wherein the magnetic layer is comprised of a metal alloy. 
     
     
       4. The method of  claim 3 , wherein the metal alloy is a cobalt-based alloy. 
     
     
       5. The method of  claim 4 , wherein the corrosion-protective agent comprises a metal salt of a perfluorinated polyether having two carboxylic acid groups. 
     
     
       6. The method of  claim 1 , wherein the underlayer comprises a chromium-containing material. 
     
     
       7. The method of  claim 1 , further comprising coating the carbon overcoat with a lubricating film of a perfluoropolyether prior to deposition of the carbon overcoat. 
     
     
       8. The method of  claim 1 , wherein the perfluorinated polyether is comprised of monomer units having the structure —CF 2 —O—, —CF 2 —CF 2 —O—, —CF(CF 3 )—O—, —CF(CF 3 )—CF 2 —O—, or a combination thereof. 
     
     
       9. The method of  claim 1 , wherein the corrosion-protective agent comprises a partially hydrogenated perfluorinated polyether comprised of monomer units of the structure —CF 2 —O—, —CF 2 —CF 2 —O—, —CF(CF 3 )—O—, —CF(CF 3 )—CF 2 —O—, or a combination thereof before hydrogenation. 
     
     
       10. The method of  claim 9 , wherein based upon the corresponding perfluorinated polyether up to about 50% of the fluorine atoms are substituted with a hydrogen atom in the partially hydrogenated perfluorinated polyether. 
     
     
       11. The method of  claim 1 , wherein the perfluorinated polyether is a linear polymer. 
     
     
       12. The method of  claim 1 , wherein the metal salt is an alkali metal salt. 
     
     
       13. The method of  claim 12 , wherein the alkali metal salt is a sodium salt. 
     
     
       14. The method of  claim 1 , wherein the perfluorinated polyether has a number average molecular weight in the range of approximately 500 to 10,000. 
     
     
       15. The method of  claim 14 , wherein the perfluorinated polyether has a number average molecular weight in the range of approximately 1000 to 5000. 
     
     
       16. The method of  claim 15 , wherein the perfluorinated polyether has a number average molecular weight in the range of approximately 2500 to 3500.